This invention relates to an exhaust system for an outboard motor, and more particularly to an improved exhaust system for an outboard motor embodying a catalyst for treating the exhaust gases.
It is well-known that outboard motors demand very compact construction. This presents a number of design challenges, particularly in designing an effective exhaust system. The exhaust system should be designed in such a way so as to provide good silencing and also good engine performance. In addition, the exhaust system must be quite compact because of the very nature of an outboard motor.
The engine performance and/or silencing can be improved by providing an exhaust pipe which delivers the exhaust gases from the exhaust port of the engine into an expansion chamber. By appropriately choosing the length of the exhaust pipe and the volume of the expansion chamber, either or both of silencing and improved engine performance can be obtained.
There is, however, also an advantage in employing catalytic treatment for the exhaust gases of outboard motors. In addition to purifying the air into which the exhaust gases pass, the catalyst can be utilized to treat the exhaust gases to remove certain harmful constituents before they are released along with the exhaust gases into the body of water in which the watercraft is operating. It is well-known in marine applications to discharge the exhaust gases from the engine into the atmosphere through the body of water in which the watercraft is operating. In this way, the body of water aids in the silencing.
However, if a catalyst is placed in the exhaust system, and particularly in the exhaust pipe, then the presence of the catalyst bed can affect both the engine performance and the performance of the silencing system.
It is, therefore, a principal object of this invention to provide an improved exhaust system for an outboard motor that will permit exhaust tuning and, at the same time, accommodate a catalyst without interfering with that tuning.
It is a further object of this invention to province an exhaust system for an outboard motor employing an expansion chamber, an exhaust pipe and a catalyst that is positioned downstream of the point where the exhaust pipe discharges into the expansion chamber.
It is also desirable with outboard motors employing catalysts to dispose the catalyst bed in such a way that it can be removed for servicing. With many of the types of construction previously proposed, however, the catalyst has been positioned in a location where it is difficult to service it.
It is, therefore, a still further object of this invention to provide an improved outboard motor having a catalyst in its exhaust system wherein the catalyst is readily accessible for servicing.
There is a particular type of outboard motor mounting system employed for certain types of watercraft that employs a transom bracket that is affixed to the transom of the watercraft and which is pivotable about a horizontally disposed axis. The outboard motor is mounted for steering movement about a vertically extending axis at the lower end of this transom bracket, and at least a major portion of the power head is disposed below the tilt pivot axis. With this type of arrangement, it is very difficult to service the outboard motor, and particularly any catalytic exhaust system for it.
It is, therefore, a still further object of this invention to provide an improved catalytic exhaust system for an outboard motor that is mounted below the transom of a watercraft and wherein the catalyst is positioned at an area in the power head where it may be conveniently serviced without requiring tilting up or removal of the outboard motor from the watercraft hull.